printk/tracing: Add console output tracing

Add a printk.console trace point to record any printk
messages into the trace, regardless of the current
console loglevel. This can help correlate (existing)
printk debugging with other tracing.

Link: http://lkml.kernel.org/r/1322161388.5366.54.camel@jlt3.sipsolutions.net

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 46 insertions, 0 deletions

diff --git a/include/trace/events/printk.h b/include/trace/events/printk.h
new file mode 100644
index 000000000000..94ec79cc011a
--- /dev/null
+++ b/include/trace/events/printk.h
@@ -0,0 +1,41 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM printk
+
+#if !defined(_TRACE_PRINTK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_PRINTK_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT_CONDITION(console,
+        TP_PROTO(const char *log_buf, unsigned start, unsigned end,
+                 unsigned log_buf_len),
+
+        TP_ARGS(log_buf, start, end, log_buf_len),
+
+        TP_CONDITION(start != end),
+
+        TP_STRUCT__entry(
+                __dynamic_array(char, msg, end - start + 1)
+        ),
+
+        TP_fast_assign(
+                if ((start & (log_buf_len - 1)) > (end & (log_buf_len - 1))) {
+                        memcpy(__get_dynamic_array(msg),
+                               log_buf + (start & (log_buf_len - 1)),
+                               log_buf_len - (start & (log_buf_len - 1)));
+                        memcpy((char *)__get_dynamic_array(msg) +
+                               log_buf_len - (start & (log_buf_len - 1)),
+                               log_buf, end & (log_buf_len - 1));
+                } else
+                        memcpy(__get_dynamic_array(msg),
+                               log_buf + (start & (log_buf_len - 1)),
+                               end - start);
+                ((char *)__get_dynamic_array(msg))[end - start] = 0;
+        ),
+
+        TP_printk("%s", __get_str(msg))
+);
+#endif /* _TRACE_PRINTK_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/printk.c b/kernel/printk.c
index 13c0a1143f49..cb8a6bd697c6 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -44,6 +44,9 @@
 
 #include <asm/uaccess.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/printk.h>
+
 /*
  * Architectures can override it:
  */
@@ -542,6 +545,8 @@ MODULE_PARM_DESC(ignore_loglevel, "ignore loglevel setting, to"
 static void _call_console_drivers(unsigned start,
                                 unsigned end, int msg_log_level)
 {
+        trace_console(&LOG_BUF(0), start, end, log_buf_len);
+
         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
                         console_drivers && start != end) {
                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {